She is one of three children in the family who, it appears, did not live to adulthood. She probably died sometime in the 1860s.
Martha is one of the mysteries of the Warner family.
The only evidence of her existence is the Canada census for 1861, in which she appears with the family and is listed as an eight-year-old female family member, born in Toronto and attending school (see “Images” below).
The census didn’t specify each family member’s relationship to the head of the family, so it is possible that Martha was a niece or a cousin, staying with the family for who knows what reason. It could even be that Martha was not James’s daughter but his half-sister, his mother Sarah‘s daughter from her second marriage to William Hudson.
There’s no evidence to support any of that and so, in the spirit of Occam’s razor, I’m opting — at least for now — for the simpler hypothesis that she was, in fact, James and Margaret’s daughter.
On the other hand, there is a problem with that.
Martha was born about 1852, when James and Margaret were both about 15. They weren’t married until 1856.
Is it possible that the baby was born, out of wedlock, to the teen couple, and that James’s widowed mother, Sarah, took Margaret and the baby in until she considered her parents were old enough to marry?
Martha doesn’t appear in the 1871 census or in any other document I’ve been able to find in years of looking. It’s theoretically possible that, at 18 (when that census was taken), she was already a married woman with a different last name and living in a different household. If that were true, it is very likely that some kind of identifying documentation would have turned up from the time of her marriage or the birth or marriage of her children. None has.
So the most likely conclusion is that Martha probably died sometime between 1861 and 1871, when between the ages of 8 and 18.